Health⏱ 5 min read
Harris-Benedict vs Mifflin-St Jeor: Which BMR Formula Is More Accurate?
The original Harris-Benedict formula has been used for decades, but the revised Mifflin-St Jeor equation is more accurate for most people. Here's the maths and when to use each.
Your Basal Metabolic Rate (BMR) is the energy your body burns at complete rest. Every TDEE and calorie target calculation starts here. But two formulas give different answers — and the difference matters.
The Original Harris-Benedict Equation (1919, revised 1984)
Men:
BMR = 88.362 + (13.397 x weight kg) + (4.799 x height cm) - (5.677 x age)
Women:
BMR = 447.593 + (9.247 x weight kg) + (3.098 x height cm) - (4.330 x age)
Example: 35-year-old woman, 65kg, 168cm
BMR = 447.593 + (9.247 x 65) + (3.098 x 168) - (4.330 x 35)
= 447.593 + 601.055 + 520.464 - 151.550
= 1,417.6 kcal/day
The Mifflin-St Jeor Equation (1990)
Men:
BMR = (10 x weight kg) + (6.25 x height cm) - (5 x age) + 5
Women:
BMR = (10 x weight kg) + (6.25 x height cm) - (5 x age) - 161
Same example: 35-year-old woman, 65kg, 168cm
BMR = (10 x 65) + (6.25 x 168) - (5 x 35) - 161
= 650 + 1,050 - 175 - 161
= 1,364 kcal/day
Difference: Harris-Benedict gives 1,418 vs Mifflin 1,364
= 54 kcal/day difference for this person
= 19,710 kcal/year (approximately 2.6 kg of fat energy)
Which Is More Accurate?
FormulaAccuracy vs Measured BMRBest For
Mifflin-St JeorWithin 10% for ~82% of peopleGeneral population, overweight individuals
Harris-Benedict (revised)Within 10% for ~75% of peopleNormal weight, lean individuals
Katch-McArdleMost accurate if body fat knownAthletic individuals with known body fat %
The Academy of Nutrition and Dietetics recommends Mifflin-St Jeor as the equation of choice for estimating BMR in non-obese adults. For athletes or those with known body fat percentage, Katch-McArdle is superior.
Katch-McArdle (Uses Lean Body Mass)
BMR = 370 + (21.6 x Lean Body Mass in kg)
Lean Body Mass = Body weight x (1 - Body fat fraction)
Example: 80kg man with 18% body fat
LBM = 80 x (1 - 0.18) = 80 x 0.82 = 65.6 kg
BMR = 370 + (21.6 x 65.6) = 370 + 1,416.96 = 1,787 kcal/day
This formula ignores gender and age (both of which affect BMR
partly through their effect on body composition) — making it
more universal when body composition is known accurately.
From BMR to TDEE
TDEE = BMR x Activity Multiplier
Sedentary (desk job, little exercise): x 1.2
Lightly active (light exercise 1-3 days/week): x 1.375
Moderately active (moderate exercise 3-5 days/week): x 1.55
Very active (hard exercise 6-7 days/week): x 1.725
Extra active (athlete, physical job): x 1.9
For our example (1,364 BMR, moderately active):
TDEE = 1,364 x 1.55 = 2,114 kcal/day
These multipliers are estimates — individual variation is high.
Track actual weight change against intake for 3-4 weeks
to calibrate your personal TDEE empirically.